What is solar cooking?
Solar cooking means cooking using sunlight and not electricity,
propane, wood, ... I've done it outdoors in below freezing temperatures
in February in Ottawa, Ontario, Canada, so chances are you can too.
Why cook with the sun?
Cook with the sun:
- for the fun of cooking a different way - For those who really
enjoy cooking different things in different ways, solar cooking
opens up a whole new range of things to try.
- for the fun of making and trying solar cookers - If you're a
DIYer there are many different types of solar cookers to make
- to save energy - The sun's energy is free. There are no electricity
bills, no propane or natural gas to buy, no wood to chop. I get
a buzz from knowing I'm getting away with not paying for energy.
- to stay cool - Solar cooking almost always means cooking outdoors.
On those steaming hot days when cooking indoors would heat the
house further, solar cooking simply won't do that.
- for the environment - No fossil fuels are used in solar cooking.
What, when and where can you cook?
You can cook anything (e.g. bread, meat, cake, eggs, rice, ...) though
for some things you have to have the right type of solar cooker.
This is the same as cooking indoors where sometimes you'll use the
burners on top of the stove, sometimes the oven and sometimes the
microwave. More about the types of cookers below.
Solar cooking can be done any time of the year as long as the sun is
out but again the type of cooker may be an issue depending on how far
north (in the northern hemisphere) or south (in the southern hemisphere
you are.) This is because of colder temperatures and because the sun is
lower in the sky in the winter. People do solar cook in the Scandinavian
countries in northern Europe in winter.
Different types of cookers
Most cookers fall into these types:
- Panel cooker - A cooker with
large reflector area that doesn't reflect all of the sun to the
cooking pot at one time. Surprisingly, this can do most of
what an indoor oven can do.
Frequency of adjustment:
Not frequent. Some need to be turned to face the sun only every
half hour or hour even.
The cooking pot is usually in a cooking bag or a glass or Pyrex
With a Pyrex container and depending on how cold it is outdoors,
this can reach temperatures of 375F (190C).
- Solar box oven - A cooker with an
insulated box and reflectors directing the sunlight into the
box through a glass window. Much of the cooking is done by the
heated air in the box. Much like an indoor oven.
Frequency of adjustment:
Not frequent. Every half hour or hour.
The box has insulation in its walls. The glass window is
typically a single pane of tempered glass.
Depending on the construction, this can reach 400F (200C).
- Parabolic dish or fresnel lens - A
cooker that directs all the sunlight to the cooking pot.
Frequency of adjustment:
Frequent. Since all sunlight is reflected to the pot, as the
sun moves, that reflected sunlight quickly move elsewhere too.
This is like putting something on a stove-top element. It
quickly boils water, and fries eggs and meat.
Where to get a solar cooker
Solar cookers can be made or bought. Panel cookers are very easy
to make, involving just cutting cardboard, aluminum foil and gluing
stuff. Solar box ovens and parabolic cookers are more work but still
buildable by anyone with a some time on their hands and no physical
handicap that would prevent it.
Purchasable solar cookers
Some solar cookers you can buy are (all prices are approximate):
- Global Sun Oven (GSO): This is a
very popular solar box oven cooker.
- Copenhagen: This is a panel cooker
with a very flexible design to accommodate all sun angles for
cooking any time of the year.
- Hot Pot: This is a panel cooker
useful for when the sun is high in the sky. If the sun is
low, as it is in the winter in many locations, then you'll
need to use something else during those times.
- Solar Burner: This is a parabolic
Make it yourself solar cookers
Here is a sample of homemade solar cookers with enough details to
make your own.
Car sunshade solar cooker
Perhaps the simplest solar cooker to make is
car sunshade solar cooker. Just go get a car sunshade,
use clips, Velcro, clothespins, ... to give it shape,
get a cooking bag to put your cooking pot in, aim it all
at the sun and you're done! The page at the above link
shows you how to do all this along with optimization tips.
Modified CooKit panel solar cooker
Another simple to make is
Modified CooKit solar cooker. All you need is a single
piece of 3'x3' cardboard, some aluminum foil and glue and
you're done! The page at the above link shows you how to make it.
Fresnel lens solar cooker
In May 2011 I noticed a derelict rear projection TV by the side of the
road and found a 2'x4' fresnel lens in it. Within weeks I'd made
this fresnel lens solar
cooker and started cooking with it.
The parts of a solar cooker
The parts of a solar cooker are as follows:
- reflectors: These are panels of
some sort that reflect sunlight to where it's needed. Their
purpose is to increase the amount of sunlight used. They
are most often either aluminum foil (from your kitchen) or
aluminized Mylar. Aluminum foil loses some of it's reflectivity
after a few years due to oxidation but is cheap and easy to
replace. The backing can be cardboard, coroplast (the corrugated
plastic that election signs are made of, or wood. The coroplast is
better than cardboard if it will be left out in the rain.
Wood is heavier.
- lenses: This refers to a
which is fun to try out but few people use it. They serve the
same purpose as reflectors, to increase the amount of sunlight
used. They do this by focusing a large area of sunlight to the
cooking pot/pan. These are available in discarded rear projection
TVs though you can buy them online too.
- insulation: Solar box oven cookers
have insulation in their walls. This slows down
the loss of heat
through the walls. Some options are:
Of the above ones, the polyisocyanurate will prevent heat loss
the best and so allow higher temperatures. Avoid using Styrofoam
or polystyrene as it has a low melting temperature.
- a few layers of corrugated cardboard with the holes in
the layers in alternating in direction,
- shredded paper,
- rigid boards of polyisocyanurate.
Another way to insulate is to put your cooking pot inside a
larger glass, usually Pyrex, container. This is often done with
very good results with panel cookers.
- glazing: Glazing is glass, Pyrex or
a cooking bag that's used to trap hot air and to prevent wind from
blowing over a cooking pot and cooling it. Examples of glazing are
- The glass window on a solar box oven. This is usually
tempered glass which is a glass that can handle higher
temperatures than regular glass. It is more expensive
though and has to be cut by the glass supplier unless you
find a piece that's a useful size.
- With panel cookers you'll often put the cooking pot inside
a larger container that is either Pyrex, glass or a cooking
bag. By using something thick like Pyrex or glass you
can get results as good as most solar box oven cookers.
- the cooking pot/pan/jar: For a panel
cooker or a solar box oven cooker it's important that the cooking
pot be a dark color because this dark coating is what turns
sunlight into heat. For parabolic or fresnel lens cooker it
doesn't matter since the concentration of sunlight is so high.
If you don't have anything that's
dark then you might be able to paint something using BBQ and Stove
spray paint, available in hardware stores.
The jar can be a mason jar. Because of the pressure that will
build up inside it's preferable to put the lid on loosely or
make a tiny hole in the top of the lid.
It's useful if the container has a transparent part somewhere so
you can look at the food without opening it. For a pot that can
be a transparent lid. For a jar you can leave a small portion
of it unpainted, around one inch square is good.
Setting up the cooker
Aiming the cooker at the sun
For a panel cooker and a solar box oven cooker your cooker doesn't
have to be pointing perfectly at the sun since the at least some
part of the panels will still reflect some sunlight at the solar cooker
over a wide range of sun angles. But a parabolic or fresnel lens
cooker must be pointing directly at the sun.
A few of the ways to aim your cooker are as follows:
- If the cooker has a flat front then make a shadow in front of
the cooker by holding your finger vertically on the ground or
table a few inches/centimeters away. If the shadow is more or
less perpendicular with the front of the cooker than the cooker
is pointing at the sun.
- Some cookers form shadows behind them that tell you when the
cooker is lined up with the sun.
- Use a special tool like sun finder.
It's basically a tool that at one end has a hole for the sunlight
to enter into. That sunlight then lands on a vertical piece of
material. The position of the sunlight on the material indicates
if the sun finder is pointing directly at the sun and if not,
can be used to tell which way to rotate it to line it up.
See this detailed
page on aiming things at the sun for more on this.
Turning sunlight into heat using an absorber
When sunlight arrives at any material, some of it is converted into
heat. The material doing this is call the absorber. The darker the
color and less reflective the material the more that's converted to
heat. For that reason, black is best when you're talking about
converting visible sunlight. A flat material is better than a more
reflective material because by definition, the reflection is sunlight
that was not turned into heat.
In a solar cooker, the absorber is the dark coating on the cooking pot.
Note that for a parabolic cooker or a fresnel lens cooker the
color and reflectivity of the cooking pot is not so important because
of the high concentration of sunlight.
Infrared light (which is not visible) has nothing to do with color
though by definition is a result of a material's interaction with
visible light. However, some materials are better than others at
absorbing infrared light. With solar cooking we don't usually worry
about that though.
Optimal reflector angles
The angle that sunlight reflects off of a surface is the same as the
angle that it arrived at. Keep this in mind when making reflectors.
Sunlight may hit your reflector, then hit another reflector further
into your cooker and then reflect right back out again without
hitting your cooking pot. That's why it's important to understand
how sunlight reflects. If your reflectors are designed properly
then all you need to do is aim the reflector at the sun and you'll
You can read a lot more about this on the
Panel cookers and solar box oven cookers are slow cookers.
The temperature isn't always as high as an indoor oven and so
cooking times are usually longer. However, this means there is
less juice and flavor lost and the result tends to taste better.
The first few times you use a new cooker, check to see if it's
lined up with the sun every fifteen minutes or so. It may not
need to be lined up each time and you'll eventually figure out
how often adjustment is required. It's not usual for adjustment
to be required only every half hour or hour.
Frying food is done with a parabolic or fresnel lens solar cooker.
These concentrate the sunlight more to a smaller area and so
produce higher temperatures on the cooking vessel.
Sun glasses, goggles
Solar cookers concentrate sunlight. The light can be so bright that
it hurts or even damages your eyes. For a panel cooker and a solar
box oven wearing sun glasses is advisable. For a parabolic or
fresnel lens cooker you should wear welding goggles. The latter
can be bought at hardware stores.
Some solar cookers are designed so that you don't see the sunlight.
For example, with a fresnel lens solar cooker that uses a mirror to
reflect the sunlight up to the bottom of the cooking vessel so you
don't see it. But when you move the vessel away you may see it then.
So it's best to wear at least sun glasses in that case.
Solar cooking is still cooking and cooking vessels get hot.
Wear oven mits.
Also, when glass is very hot and you touch it
with a cool finger, the glass may break due to the temperature
difference. I've shattered one Pyrex lasagna pan and cracked
one mason jar just by a light touch of my finger. This can be
prevented by wearing oven mits.
Safe cooking temperatures to avoid bacteria
When cooking food it must get hot enough to kill any
bacteria. Also, there are temperatures at which some bacteria thrive.
In a typical indoor oven, when you set the dial you can be
reasonably sure the temperature will be what you set it to.
With solar cooking you have to be more watchful.
Make sure your food cooks about 140F (60C) for more than ten
If using a panel cooker, you can monitor the temperature by putting
an oven thermometer inside the Pyrex or glass container or cooking
bag. With a solar box oven cooker put it in the oven bu such that it's
visible through the window. To look at it you can always rotate the
oven away from the sun briefly so you don't get blinded.
It's best if the thermometer not get direct sunlight otherwise
the sunlight may be heating the thermometer directly.
The temperature inside the cooking vessel will likely be lower
than the temperature of the food inside the cooking vessel.
But this is the same for an indoor oven too.